1. Field of the Invention
The present invention relates to a light emitting appliance, and more particularly to a light emitting appliance having unit light emitting devices each with at least three light emitting elements with substantially different emitting colors.
2. Description of the Related Art
As an example of an image display, a full-color image display using an organic EL (electroluminescence) has been proposed. FIG. 16A schematically shows the configuration of a display panel DP used in such a full color image display.
The display panel DP is provided with a glass substrate GL. On the glass substrate, a large number of anodes ANO's are arranged in stripes. On the anodes ANO's, a red light emitting layer R, a green light emitting layer G and a blue light emitting layer B are cyclically arranged in stripes in this order in stripes in a direction orthogonal to the anodes ANO's. Cathodes CR, CG and CB are arranged on and along the red light emitting layer R, green light emitting layer G and blue light emitting layer B, respectively.
A set of red light emitting layer R, green light emitting layer G and blue light emitting layer, which are sandwiched between a single anode ANO and a set of cathodes CR, CG and CB, constitute a unit light emitting device UL. Namely, the display panel DP is composed of a larger number of unit light emitting devices UL's arranged in a matrix form.
By adjusting the luminance of the red light emitting layer R, green light emitting layer G, blue light emitting layer B, the unit light emitting device UL can be caused to emit light at any color. By causing a large number of the unit light emitting devices UL's arranged in a matrix form to emit light, a full color image with any desired full color image can be displayed.
However, the above conventional full color image display using the organic EL presents the following problem. FIG. 16B is an equivalent circuit diagram of the unit light emitting device UL constituting the display panel DP shown in FIG. 16A. As seen from FIG. 16B, in order to cause the unit light emitting device UL to emit light at any color in the display panel DP, four terminals (one anode ANO and a set of cathodes CR, CG and CB) are required.
This makes the appliance structure inclusive of its wiring complicate, thus making it difficult to realize the display at a high density. Particularly, where a large number of display panels DP's shown in FIG. 16A are used in order to constitute a full color image display having a large number of pixels, the structure inclusive of the wiring becomes more complicate, thus making it further difficult to realize the display at a high density.
Further, in the display panel DP, three light emitting layers arranged at intervals on a plane, i.e. a red light emitting layer R, green light emitting layer G and blue light emitting layer B constitute a unit light emitting device UL. Therefore, there was a limitation to realize the high density of the display.
Further, generally, the luminance of each of the red light emitting layer R, green light emitting layer G and blue light emitting layer B are not equal on the same condition. In order to approximate the luminance of each light emitting layer to one another, the light emitting are, i.e. width of each light emitting layer, is made different. If the luminance of the red light emitting layer 1 is the lowest, that of the blue light emitting layer 2 is intermediate and that of the green light emitting layer 3 is the highest, as seen in FIG. 17, the width of the red light emitting layer 1 is made the largest W1, that of the blue light emitting layer 2 is made intermediate W2, and that of the green light emitting layer 3 is made the smallest W3. However, in such a technique, the green light emitting layer 3 having the smallest width W3 is a bottleneck in fabrication, and the presence of the red light emitting layer 1 further accelerates the difficulty of the display at a high density.